This invention relates to improvements in a fuel vapor treatment device configured to adsorb fuel vapor from a fuel tank and the like of an automotive vehicle and release the adsorbed fuel to be combusted in an engine during operation of the engine.
In general, a fuel vapor treatment device or canister of this type includes a casing which is formed with a charge port connected to the fuel tank, a purge port connected to an intake side of the engine, and an atmospheric air port through which atmospheric air is introduced. A fuel vapor adsorbing material such as activated carbon or the like is filled inside the casing. The adsorbing material is isolated from atmospheric air introduced from the atmospheric air port by a filter, and therefore dust contained in atmospheric air is trapped by the filter.
Now, in the fuel vapor treatment device of this kind, the amount of dust trapped in the filter gradually increases with lapse of time so that the filter may be clogged. In case that severe clogging of the filter occurs, a flow resistance between the atmospheric air port and the purge port increases during purging of fuel vapor adsorbed in the adsorbing material, thereby making it impossible to sufficiently purge the fuel vapor out of the fuel vapor treatment device.
In view of the above, Japanese Patent Provisional Publication No. 11-200963 proposes such a device that the cross-sectional area (perpendicular to the axis) of the filter on the side of the atmospheric air port is enlarged relative to the cross-sectional area of a section filled with the adsorbing material. Also in this case, the filter may be clogged when a large amount of dust is sucked through the filter.
In order to cope with the above problems, Japanese Patent Provisional Publication Nos. 2001-317418 and 2001-323846 propose the following fuel vapor treatment devices: A passage arrangement is provided in such a manner as to suck atmospheric air from the lower side of a filter so that dust adhered to the filter is dropped under the action of gravity, engine vibration and the like and removed.